Kelmet, a soft alloy on whose surface a Pb based overlay-alloy is plated, is widely used for sliding bearings for automobiles.
On the other hand, resin-coated bearing materials are also known. Japanese Unexamined Patent Publication No. 60-1424 proposes a sliding bearing in which solid lubricants such as molybdenum disulfide, tungsten disulfide and graphite are bonded by phenol resin, polyamide imide resin and the like on uneven surfaces formed on the iron, copper or aluminum-based backing metal. Alusil alloy is shown as an embodiment of the aluminum-based metal.
Bearings with a coating consisting of a solid lubricant are also known. Japanese Unexamined Patent Publication No. 58-81220, is related to an application of the present applicant and proposes a thrust bearing. In this bearing, a solid-lubricant film is formed on the metallic blank material or on the manganese phosphate or soft nitriding coating applied on the metallic blank material having enough strength, such as carbon steel (SPCC) and aluminum alloy which contains as an alloying element one or more of 0-10% of Sn, 0-5% of In and 0-5% of Pb, and 0-3% of Cu and/or Mg, and 10% or less of one or more of Cr, Si, Mn, Sb, Fe, and Ni as an optional element.
Recently automobile engines have achieved outstanding high performance through high power and high rotation. The conventional kelmet alloy with the overlay satisfies the compatibility for the high performance engines, but incurs the problem that the lubricating oil deteriorates to form corrosive media, by which the overlay is liable to be attacked. Application of an overlay on the aluminum alloy has been considered as a measure to enhance compatibility, but the problem of poor corrosion-resistance then arises. An intermediate layer consisting of metal with excellent adhesion, such as Cu, Ni and the like, is formed on the lining (bearing alloy) when the overlay is applied. The intermediate layer itself has a poor friction property and is thus disadvantageous lo in the light of seizure.
The compatibility of an overlay at the initial period of operation seems to be mainly due to the plastic deformation of the soft metal in conformity with the shaft and, to a lesser degree, to the wear of the soft metal as it conforms to the shaft. However, the plastic deformation of the overlay is limited by its material property. The problem of local-contact seizure is likely to occur at points of contact between the overlay and the shaft under the present situation of engine operation and machining accuracy of the engine parts. More specifically, since a mechanical test under static conditions has revealed that the maximum limit of plastic deformation is from 50 to 80%, the local contact, which is approximately of the same degree as this limit, cannot be absorbed by the plastic deformation.